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FDSC 300 > Lecture 11 - CHO Chemical Analysis > Flashcards

Lecture 11 - CHO Chemical Analysis Flashcards

1
Q

True or false: Proximate analysis incorporates CHO

A

False…. kinda
CHO is not measured directly but instead achieved by subtracting 100% by the summed percentages of moisture, ash, protein, fiber, and fat

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2
Q

what role do CHO play in food?

A

metabolic energy, if digestible
if not:
- mouthfeel (bulkiness, body, viscosity, stability to emulsions and foams)
- water-holding capacity
- stability to freezing and thawing
- browning
- textures (crispness to smooth, soft gels)
- lower water activity/inhibit microbial growth

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3
Q

how are CHO classified according to WHO and FAO?

A

size
sugars (DP 1-2)
Oligosaccharides (DP 3-9)
Polysaccharides (DP>9)

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4
Q

how are CHO classified according to international nomenclature rules?

A
  • oligosaccharides = 2-10 (sometimes 20) sugar units

- polysaccharides = 30-60,000 or more monosacch

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5
Q

arabinose is a

A

monosaccharide

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6
Q

xylose is a

A

monosaccharide

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7
Q

raffinose is a

A

trisaccharide

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8
Q

true or false: disaccharides and trisaccharides are considered oligosaccharides

A

true

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9
Q

list some homopolysaccharides

A

starch, cellulose, glycogen (only composed of glucose)

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10
Q

list some heteropolysaccharides

A

pectin, hemicellulose, gums

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11
Q

how are CHO present in foods?

A
  • unbound
  • physically associated to other molecules (e.g. starch granules)
  • chemically bound (glycolipids, glycol-proteins)
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12
Q

why is CHO determination relevant?

A
  • nutrition labelling
  • detection of adulteration
  • food quality (sweetness, appearance, stability, texture)
  • food processing (affects efficiency)
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13
Q

true or false: proximate analysis is a widely accepted way of determining sugar content in food

A

nah. it’s erroneous due to experimental errors of any of the other methods. best do it directly.

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14
Q

name the 5 categories of methods used for CHO determination

A
  • chemical
  • physical
  • enzymatic
  • instrumental
  • immunoassays
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15
Q

chemical methods include what kind of methods

A

colorimetric, titration, and gravimetric methods

we got 5 individual methods to memorize from this unit

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16
Q

what are the colorimetric methods of interest eh?

A
  • phenol-sulfuric acid method
  • anthrone method
  • Somogyi-Nelson Method
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17
Q

what’s the titration method of interest called?

A

Lane-Enon Method

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18
Q

what’s the gravimetric method of interest called?

A

Munson-Walker Method

19
Q

the phenol-sulfuric acid method determines what?

A

total carbohydrates

20
Q

describe how the phenol-sulfuric acid method works

A

1) add sample to H2SO4 under heat
2) furan components are produced
3) add Phenol to induce condensation rxns
4) yellow-gold color is produced
5) measure with spec at 490 nm

21
Q

the phenol-sulfuric acid method (does/does not) involve stoichiometric reactions

A

does not

22
Q

with the phenol-sulfuric acid method, the extent of the reaction is a function of the __________

A

structure of the sugar

23
Q

true or false: the phenol-sulfuric acid method is simple, sensitive, accurate, and specific.

A

true!

24
Q

with the phenol-sulfuric acid method, what do you do if different sugars are found?

A

use glucose to prepare a standard curve

25
Q

true or false: the phenol-sulfuric acid method can also be used to determine sugar alcohols

A

false. does not produce a positive result

26
Q

the Anthrone method measures what?

A

total carbohydrate

27
Q

describe the Anthrone method

A
  • CHO are dehydrated by strong acids to produce a furan component
  • furan components react with Anthrone reagent
  • blue green color formed
  • measure abs at 620 nm
28
Q

draw the structure of HMF (hydroxymethylfurfural)

A

yikes okay (looks like someone squared up)

29
Q

Fehling’s test measures what?

A

presence of aldehydes

30
Q

describe Fehling’s test

A
  • copper II is reduced to copper oxide
  • this shifts color from blue to brick red
    Reagents:
    A: CuSO4*H20 in d-water with 2 drops of dilute sulfuric acid
    B: Potassium tartrate and NaOH in d-water
31
Q

what’s the somogyi-nelson method?

A

fehling’s method: who are you?
somogyi-nelson method: i’m you but better
uses enzymes before addition of reagent so oligo and polysaccharides can be determined

32
Q

somogyi-nelson method measures what?

A

reducing sugars

33
Q

describe the somogyi-nelson method

A

Reagents:
- NaOH
- CuSO4
- ammonium molybdate
- sodium arsenate
(the last 2 form an arsenomolybdate complex)
1) solution of Cu2SO4 and NaOH is added to solution of reducing sugars
2) mixture heated in boiling water bath
3) add the other 2 reagents
4) arsenomolybdate complex is reduced by Cu(I) to a stable blue color
5) measure @ 520 nm with spec

34
Q

Lane & Eynon method measures what?

A

reducing sugars

35
Q

the Lane & Eynon method is based on the _____ action of CHO toward certain _____ _____

A

reducing; metallic salts

36
Q

describe the Lane & Eynon method

A
  • titrate CHO against known concentration of CuSO4 in alkaline condition
  • use methylene blue as indicator
  • end point indicated by solution turning colorless
37
Q

true or false: the Lane & Eynon method can directly determine concentration of non-reducing sugars

A

false

38
Q

limits of the Lane-Eynon method?

A
  • results depend on precise reaction times. conditions must be controlled (temp, reagent concentrations)
  • can’t distinguish between types of reducing sugars
  • can’t directly determine concentration of non-reducing sugars
  • susceptible to reducing molecules
39
Q

The Munson & Walker method measures what?

A

reducing sugars

40
Q

describe the Monson & Walker method

A
  • Sample w/reducing sugar is introduced to CuSO4, base, and heat
  • oxidized sugar plus CuO2 precipitate is formed
  • weigh precipitate
    amount of precipitate is directly related to concentration of reducing sugars in sample
41
Q

limits of the Munson & Walker method?

A

(same as Lane & Eynon)

  • depends on precise rxn times
  • can’t distinguish between different types of reducing sugars
  • can’t directly determine concentration of non-reducing sugars
  • susceptible to interference from other reducing molecules
42
Q

which method is more reproducible and accurate? Lane & Eynon or Munson & Walker?

A

Munson & Walker

43
Q

limits of the phenol-sulfuric acid method?

A
  • requires clear solution

- standard curve must be made with same exact mixture of CHO, ratios and all that occur in the sample

44
Q

what do you do if there’s interfering reducing compounds for your reducing sugar methods?

A

extract em

FDSC 300 (9 decks)

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